The present invention relates to a copier, printer, facsimile machine, or other such image forming apparatus employing electrophotographic image forming method(s); more particularly, the present invention pertains to an image forming apparatus equipped with transfer apparatus(es) transferring, onto transfer medium/media, development image(s) formed on image carrier(s).
In an image forming apparatus employing an electrophotographic photosensitive body (hereinafter “photosensitive body”) as image carrier, the surface of the photosensitive body is first uniformly charged by a charging apparatus, and the surface of the photosensitive body is then exposed by an optical write device to form a an electrostatic latent image. At a development apparatus, the electrostatic latent image is then developed by means of developer (toner), and at a transfer apparatus, the electrostatic latent image is transferred onto transfer medium/media (e.g., recording paper) that has been transported thereto; following which, the electrostatic latent image is fused onto transfer media by means of a fusing apparatus and is provided to a user or the like as media on which an image has been formed.
Transfer methods in which transfer roller(s), transfer brush(es), transfer block(s), and/or other such transfer body or bodies is/are pressed against and/or is/are brought in proximity to photosensitive body surface(s) have in recent times frequently come to be employed during transfer operation(s) in which development image(s) (toner image(s)) is/are transferred. This is because such methods are among those which are more considerate of the environment in that ozone emissions are generally reduced as compared with conventional electrostatic transfer methods making use of electric discharge from a corona discharge wire.
However, when employing the aforementioned transfer methods in which transfer roller(s), transfer brush(es), transfer block(s), and/or other such transfer body or bodies is/are brought in proximity to and/or is/are pressed against photosensitive body surface(s), spatial tolerances for transport of transfer medium/media are reduced, requiring increased transport accuracy, as compared with conventional electrostatic transfer methods employing corona discharge wire.
That is, unless transport accuracy is increased, this will invite problems in which transfer medium/media deviate from transport path(s), increasing likelihood of contact with nearby component(s) and/or transfer medium/media fold and/or jam, as well as problems in which development image(s) on transfer medium/media is/are disturbed as a result of contact and/or in which residual toner remaining on photosensitive body surface(s) and/or toner that has been scattered thereabout and/or the like adheres to transfer body surface(s), adversely affecting transfer action. Moreover, due to the fact that a wide variety of circumstances can be envisioned with respect to ambient conditions such as humidity and the like as well as transfer medium stiffness and so forth, there would be difficulty in achieving proper transport over a broad range of conditions.
As one specific example, after the trail edge portion of the transfer medium has passed through the region at which the photosensitive body opposes the transfer body, it is possible that the trail edge portion of the transfer medium will press against or come in contact with the surface of the transfer body and that toner will adhere to the transfer body. If the trail edge portion of a subsequent transfer medium similarly presses against or comes in contact with the transfer body, then toner adhering to the transfer body can adhere to the trail edge portion of the subsequent transfer medium. And there has been the problem that when fusing of the transfer medium takes place with toner adhering to the trail edge portion thereof, the trail edge portion of the transfer medium becomes dark and soiled.
Image forming apparatuses have therefore been proposed, for example, in which the trail edge portion of the transfer medium is prevented from coming in contact with the transfer body as a result of provision of transfer medium guide member(s) downstream in the transfer medium transport direction from the transfer body (see, e.g., Japanese Patent Application Publication Kokai No. 2002-278310).
However, the image forming apparatus indicated in the aforementioned Japanese Patent Application Publication Kokai No. 2002-278310 has had problems such as the following. Where attempts have been made to provide transfer medium guide member(s) at location(s) such as would permit sufficient distance to be maintained between the photosensitive body and the trail edge portion of the transfer medium, there has been the problem that the transfer medium is improperly guided as the lead edge portion of the transfer medium is made to advance toward the fusing operation which is subsequent thereto, impairing ability to achieve proper transfer medium transport characteristics. In contrast, where attempts have been made to ensure proper transport medium transport characteristics, there has been the problem that it has not been possible to maintain sufficient distance between the photosensitive body and the trail edge portion of the transfer medium, meaning that there has been inadequate effect with respect to prevention of soiling of the trail edge portion of the transfer medium.
The present invention was conceived in light of the foregoing problems in the conventional art, it being an object thereof to adequately ensure proper transfer medium transport characteristics and completely prevent contact between photosensitive body or bodies and transfer medium trail edge portion(s), and to therefore provide an image forming apparatus permitting satisfactory image formation.